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Old 29-09-2015, 22:23   #1
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How to get Tachometer with Alternator off?

I'm running a 400 ah LiFePo4 house bank and need to turn the engine alternator off when cycling the batteries. Problem is that my 2012 Yanmar 4JH4-TE uses the alternator feed to run the tach & hour meter. So, when I switch the ignition circuit off, I lose the tach and hour meter on the digital panel. I've been told one solution is to fit a mechanical style aftermarket tach (e.g., magnetic pickup sensor attached to flywheel etc.), but don't find any offerings in the usual places.

Wondering what other LiFePo4 users are doing?
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Old 29-09-2015, 22:32   #2
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re: How to get Tachometer with Alternator off?

where is your engine battery in this? the alternator should contine to charge that when the house is disconnected.
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Old 29-09-2015, 22:33   #3
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re: How to get Tachometer with Alternator off?

I have seen a couple of people post this and claim it works really well. I have no experience with it though.

Design Technology, Inc., Home of the Tiny-Tach - Diesel Tiny-Tach Tachometer
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Old 29-09-2015, 23:05   #4
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re: How to get Tachometer with Alternator off?

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Originally Posted by smac999 View Post
where is your engine battery in this? the alternator should contine to charge that when the house is disconnected.
I have a reserve bank of FLA batteries, but don't use a "starting" battery, as it's unnecessary weight IMO. That said, you can't mix the two different battery chemistry types with my charge controller.
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Old 30-09-2015, 09:09   #5
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Re: How to get Tachometer with Alternator off?

You raise a good point about the start battery. I have wondered about LiFe04 but certainly would not consider having no start battery for the obvious safety reasons. How do other people resolve this one, how do LiFe perform as start batteries?
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Old 30-09-2015, 13:45   #6
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Re: How to get Tachometer with Alternator off?

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Originally Posted by SailorGerry View Post
I'm running a 400 ah LiFePo4 house bank and need to turn the engine alternator off when cycling the batteries. Problem is that my 2012 Yanmar 4JH4-TE uses the alternator feed to run the tach & hour meter. So, when I switch the ignition circuit off, I lose the tach and hour meter on the digital panel. I've been told one solution is to fit a mechanical style aftermarket tach (e.g., magnetic pickup sensor attached to flywheel etc.), but don't find any offerings in the usual places.

Wondering what other LiFePo4 users are doing?
My 1998 Yanmar 2GM 20 has a magnet / sensor on the flywheel for the tach. Its very accurate. I'm surprised that your bigger, 14 year younger Yanmar is still using an alternator feed. Are you sure that you haven't got a flywheel magnetic pickup which is sitting unused?
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Old 30-09-2015, 16:17   #7
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How to get Tachometer with Alternator off?

Quote:
Originally Posted by SailorGerry View Post
I'm running a 400 ah LiFePo4 house bank and need to turn the engine alternator off when cycling the batteries. Problem is that my 2012 Yanmar 4JH4-TE uses the alternator feed to run the tach & hour meter. So, when I switch the ignition circuit off, I lose the tach and hour meter on the digital panel.

Wondering what other LiFePo4 users are doing?

How long does it take to switch batteries, that you can't live without a tach?

Why are you switching batteries? You have two lifepo4 banks?

Are you just turning the ignition circuit off? If so you are losing everything including oil pressure warnings. You can stop the charge by putting a switch in the alternator field wire. This is what we do. Our 3gm30 yanmar has the flywheel tach, so we don't lose it. Charge system warning comes on though, in case you forget to turn it back on.

First season almost complete with our 400 ah lifepo4, so far could not be happier.

As separate start battery, we carry a portable battery jump starter, works fine in testing, even better if you decompress a couple of the cylinders to get the flywheel going.



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Old 30-09-2015, 19:25   #8
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Re: How to get Tachometer with Alternator off?

My 1998 4JH2TE has the 80A alternator, which has a separate voltage sense input (mine driven from downstream of the diode battery combiner, to account for the voltage drop across it). Raising the sense input voltage reduces the alternator output as it sees a fully-charged battery. Put ~15V on the sense lead and alt output goes to zip.
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Old 30-09-2015, 19:47   #9
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Re: How to get Tachometer with Alternator off?

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Originally Posted by roland stockham View Post
You raise a good point about the start battery. I have wondered about LiFe04 but certainly would not consider having no start battery for the obvious safety reasons. How do other people resolve this one, how do LiFe perform as start batteries?
making consession for the weight of a starting battery IMO is like considering the weight of a ditch bag as too much. there are a lot of things attached to the house batteries that can unexpectedly drain the batteries...then how do you start the engine? Sounds like your trying to invent a square wheel.
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Old 30-09-2015, 20:55   #10
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Re: How to get Tachometer with Alternator off?

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making consession for the weight of a starting battery IMO is like considering the weight of a ditch bag as too much. there are a lot of things attached to the house batteries that can unexpectedly drain the batteries...then how do you start the engine? Sounds like your trying to invent a square wheel.


Not disagreeing, you need a way to start the engine. The problem is how to charge a separate LA bank when your other charging devices, regulators, etc. are setup for lifepo4. If it is hardwired to the starter it is even worse because, because it will get depleted. But even so, LA batteries discharge themselves over time.

In my mind a few of choices exist:
1. Build a much smaller Lifepo4 bank, and charge it just like you would your house bank, but even eliminating BMS systems, etc this would be very expensive.
2. Have a cold cranking amp LA battery (car size), wire it through a two way switch to the starter, figure out how to charge it. 120 volt charger, from an inverter, maybe? Small dedicated solar trickle charger?
3. Carry a jump start battery available almost anywhere, use that if you do something boneheaded to disable you LI pack. These have charging circuits built in and you can recharge it from you house bank directly once the engine is up and running.


So we can presume 3 is the cheapest, but the slowest to engage when house bank is dead. House bank dying and emergency (under a couple of minutes vs. say 15 minutes) need for starting the engine, are in most cases two separate events. I know anything can happen, but the engine could just fail to start for any number of reasons, when you need it most, this is just one of them. If you are approaching land, expect bad weather, nightfall, etc. your checklist should include ensuring your batteries are fully charged, you have time to plan for this, and if the LI bank can't start the engine, you get you jump start kit installed. Also if your engine engine has decompression valves, you need very little amperage to get the flywheel going, so just doing that is likely to fire it up. I know this because we lived with nearly dead batteries for more time than I would like. Having to decompress it every time we started engine. This is what prompted our power system reengineering.










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Old 30-09-2015, 21:20   #11
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Re: How to get Tachometer with Alternator off?

what is the absorb voltage set point of your alt regulator right now?


I would just run the alt through the com of a 1,all,2 switch, and switch it to the FLA batteries if you don't want the li to charge. then it'll keep your spare bank charged and your tach working. I doubt the voltage is much difference. but I could be wrong.
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Old 30-09-2015, 21:24   #12
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Re: How to get Tachometer with Alternator off?

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The problem is how to charge a separate LA bank when your other charging devices, regulators, etc. are setup for lifepo4.
something like an echocharger or duo charger would likely work just fine. the duo charger could probably even go the other way too as I think it's adjustable.
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Old 30-09-2015, 21:32   #13
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Re: How to get Tachometer with Alternator off?

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how do LiFe perform as start batteries?
Perfectly.

Actually, better than perfectly, almost NO voltage sag during cranking regardless of state of charge.

I have one bank on my boat of 200 aH LiFePo4's and have all the toys aboard.

We live exclusively on solar when on the boat for weeks at a time.
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Old 30-09-2015, 21:39   #14
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How to get Tachometer with Alternator off?

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something like an echocharger or duo charger would likely work just fine. the duo charger could probably even go the other way too as I think it's adjustable.

Nope, you never charge at anything above 13.9. LA does not receive proper charging at that. Echo charger can't change charge voltage, just at what point it kicks in.


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Old 30-09-2015, 21:40   #15
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How to get Tachometer with Alternator off?

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what is the absorb voltage set point of your alt regulator right now?


I would just run the alt through the com of a 1,all,2 switch, and switch it to the FLA batteries if you don't want the li to charge. then it'll keep your spare bank charged and your tach working. I doubt the voltage is much difference. but I could be wrong.

LI wants 13.9 bulk, 13.8 absorb. Not enough to properly charge and maintain a LA battery. If you already have the LA, the switch and the wiring then look at point 2 of my post #10.


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